The pen of a poet (5)
I believe the answer is:
pound
I believe this clue is a double definition.
'the pen' is the first definition.
(thesaurus)
'a poet' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for pound that I've seen before include "Where vehicles may be reclaimed" , "Powder - 16 oz - 100p" , "L" , "Repeatedly strike" , "Quid" .)